Polyethylene may be used in manufacturing molded articles, such as thin wall containers (e.g., lids and tubs), caps, closures, or fitments, to achieve adequate stiffness. However, the industry often desires to decrease the amount of material in molded articles to reduce the weight and lower shipping costs. Reducing the weight of molded articles is not without its drawbacks. A decrease in the barrier performance is often seen when reducing the weight of molded articles. Barrier performance of the molded article can affect the prevention of product spoilage. Even minimal reductions in the molded article's barrier to air, moisture and other contaminants can cause a dramatic impact on the shelf life of a product.
To combat these deficiencies, nucleating agents can be used. Typical nucleating agents may include one or more of metal carboxylates, metal aromatic carboxylate, hexahydrophthalic acid metal salts, stearates, organic phosphates, bisamides, sorbitols, and mixtures thereof. For example and not by way of limitation, suitable commercial examples of nucleating agents may include one or more of Hyperform® HPN-68L (which is primarily a disodium salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid), Hyperform® HPN-20E (which is a mixture of zinc stearate and a calcium salt of 1,2-cyclohexanedicarboxylic acid), or Hyperform® HPN-600ei (which is primarily a disodium salt of bicyclo[2.2.1]heptane-2,3-dicarboxylic acid), or Hyperform® HPN-210M, which are available from Milliken Chemical (Spartanburg, S.C.).
However, these additives can be very expensive, difficult to disperse in polyethylene, and require greater amounts to provide suitable barrier performance, which can present a problem for food contact applications where compliance with government regulations is required.
Accordingly, it may be desirable to produce polyethylene compositions for use in manufacturing molded articles having improved barrier performance.